In System Architecture Evolution (SAE)/LTE, Mobility Management Entity (MME) performs access control for the target CSG HeNB when there is a handover required from the source eNB/HeNB which UE attached to. MME determines if UE can access the target CSG HeNB based on the CSG ID received from Handover required message and stored CSG subscription data for the UE. If the access control fails, MME sends Handover preparation failure to source eNB/HeNB (see Non Patent Literature (NPL) 1). Source eNB/HeNB will then not send Handover command to UE therefore handover procedure will not be carried on.
However, the discarded handover is caused by access control failure, which can be caused by out of date CSG subscription data in MME and/or UE. Firstly, MME should verify if its CSG subscription data is still fresh, if not, it should retrieve a fresh one from Home Subscriber Server (HSS), and according to which MME should perform access control. If access control failed, source eNB/HeNB should indicate UE about the access control failure so that UE can update its whitelist.